The legislation requires a system that, if triggered by an authorized user, will lock a handset to essentially make it useless. The feature must be installed and activated in new smartphones, but users will be able to deactivate it if they desire, and it must be resistant to attempts to reinstall the operating system.

Police can also use the tool, but only under the conditions of the existing section 7908 of the California Public Utilities Code. That gives police the ability to cut off phone service in certain situations and typically requires a court order, except in an emergency that poses “immediate danger of death or great bodily injury.”

The law doesn’t specify how the system locks the phone, nor what happens to the data on the phone when it’s locked. Each manufacturer can come up with their own system.

The law follows pressure on phone makers from the state’s law enforcement community to do something about rising incidents of smartphone theft, which has become one of the most prevalent street crimes in the state.

Apple has already responded and added a feature called Activation Lock into its iOS 7 operating system, which meets all requirements of California’s kill switch law bar one—it doesn’t come enabled in new phones. That will have to change.

Both Google and Microsoft have said they are introducing similar features in upcoming revisions to their smartphone operating systems.

“California has just put smartphone thieves on notice,” California State Senator Mark Leno, the sponsor of the legislation, said in a statement. “Our efforts will effectively wipe out the incentive to steal smartphones and curb this crime of convenience, which is fueling street crime and violence within our communities.”

The law makes California the second state in the U.S. to pass legislation aimed at reducing smartphone theft. Minnesota passed a law in June, but it doesn’t require the kill switch to be enabled as default. Law enforcement says that’s key because it will increase the chance that a new smartphone has the kill switch enabled, hopefully reducing its attractiveness to thieves.

The kill switch function was actively opposed by the wireless industry until earlier in 2014, when carriers and their lobbying group reversed course and came out in favor of the plan. They received more persuasion in the form of two additional bills introduced to the U.S. House of Representatives and the Senate.

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